INTRAPOPULATIONAL SIZE STRUCTURE OF THE MONOCARPIC SPECIES SAXIFRAGA-MUTATA AND ITS RELATIONSHIP TO SUCCESSION

The monocarpic Saxifraga mutata, a locally endangered species in Centr al Europe, grows at sites which are strongly influenced by erosion. Th ree populations of S. mutata were investigated in Northeastern Switzer land. Each of the localities is characterized by a succession series f rom almost bare slopes to sparse Pinus-woods (Molinio-Pinetum). Rosett e diameters of vegetative and generative individuals showed L-shaped d istributions in two populations. A normal-shaped distribution, indicat ing low rejuvenation, was found in the third population. Rosette diame ters were significantly correlated with other fitness-related traits s uch as number of flowers, number of leaves, and flowering stem length. A reproductive threshold size of c. 4 cm in rosette diameter was reco rded. Investigations of size structures in plots of 1 m(2) demonstrate d that rosette size, rosette density, recruitment, and frequency of fl owering individuals were closely related to successional stages as wel l as intensity and frequency of erosion. Maintenance of local populati ons of S. mutata depends on the balance between erosion and succession . Landscape dynamics must be warranted in order to conserve this speci es.